914 
Hydrocyanic  Acid. 
f  Am.  Jour.  Pharm. 
(     December,  1920. 
saturated  solution  of  boric  acid  to  the  liquid  before  titration.  I  have 
not  verified  this  last  statement. 
EXPERIMENTAL. 
The  results  given  were  obtained  in  1909.  This  work  was  an 
extension  of  some  work  on  cyanide  solutions,  in  which  the  ammoniacal 
iodide  process  had  given  the  best  results  as  compared  with  other 
methods. 
As  a  standard  for  comparison  the  HCN  was  determined  gravi- 
metrically  by  weighing  as  silver  cyanide,  and,  as  a  check,  igniting 
the  silver  cyanide  to  constant  weight,  and  weighing  again  the  residual 
metallic  silver.  To  prevent  loss  by  volatilization  the  acid  was  added 
to  sufficient  ammonia  in  a  stoppered  flask,  after  previously  ascer- 
taining the  weight  of  flask  +  NH3  solution  and  the  total  weight  again 
found.  The  mixture  was  transferred  to  a  beaker,  excess  of  silver 
nitrate  solution  added,  and  then  the  whole  acidified  slightly  with 
dilute  HNO3. 
The  precipitate  was  collected  on  asbestos  in  a  Gooch  crucible, 
dried  at  ioo°-io5°  C.  to  constant  weight.  To  convert  the  AgCN 
to  silver,  the  Gooch  crucible  was  transferred  to  an  ordinary  crucible 
of  the  same  shape  in  which  it  just  fitted,  and  ignited  fairly  strongly  to 
constant  weight.  In  the  volumetric  work  (Series  A)  from  50-60 
Gms.  of  the  acid  were  weighed  out  similarly  into  a  flask  containing  the 
NaOH  or  NH3,  respectively,  and  the  whole  diluted  in  a  measuring 
flask  to  a  definite  volume,  aliquot  portions  being  drawn  off  for  the 
titration. 
The  mean  results  by  the  gravimetric  process  may  be  taken  as 
very  close  to  the  true  strength  by  weight  of  HCN. 
In  Series  A,  below,  the  individual  determinations  were  made  on 
the  same  day  as  the  gravimetric  process,  since  the  solution,  even  after 
mixing  with  the  alkali,  is  not  of  constant  strength. 
The  results  may  be  regarded  as  fairly  comparative.  The  amount 
of  N / 10  silver  solution  varied  from  40  to  46  Cc,  so  that  the  errors 
of  reading  are  negligible  in  final  results. 
Measuring  flasks,  burettes,  etc.,  were  standard  (verified  at 
Charlottenburg) . 
The  hydrocyanic  acid  used  was  prepared  in  the  laboratory  (from 
pure  materials,  by  distilling  K4FeCy6  with  dilute  sulphuric)  in  order 
to  ensure  absence  of  HCl  (a  trace  of  which  is  said  to  be  added  to  the 
commercial  acid). 
